Method for communicating indoor location to an emergency service system

ABSTRACT

A method for communicating location to an emergency service system. A wireless communication device (WCD) such as a cell phone attains a GPS location fix when outdoors and then uses a compass and pedometer to determine its direction(s) and distance(s) of travel reaching a position inside a building. When a user of the WCD places an emergency call, the WCD conveys an indication of its indoor location in a signaling message to an emergency service center, and an intermediation system such as an IMS system translates the indoor location indication to a textual description of a portion of the building (e.g., room, cubicle, zone, etc.) that encompasses the indicated location. An emergency service operator can thus receive the building portion description, to facilitate emergency service response. Further, a similar process can then be repeated during the call, to provide an updated building portion description to the operator.

BACKGROUND

For certain types of calls, it can be advantageous to obtain informationregarding the location of the caller. For example, when a Public SafetyAnswering Point (PSAP) answers an emergency-services call, it isdesirable for the PSAP to be able to automatically determine thelocation of the caller in order to quickly dispatch assistance to thatlocation. For calls made from landline phones, which typically havefixed locations, the PSAP usually determines the caller's location basedon the calling-party number included in the SS7 or other signaling thatis used to route the call to the PSAP. In particular, the PSAP mayconsult a database, such as an Automatic Location Identification (ALI)database, to determine what physical location is associated with thelandline calling-party number.

For calls made using a wireless phone and a wireless wide area network(WWAN), however, difficulty can arise because the wireless phone ismobile and is thus not associated with a fixed location. Furthermore,for calls made using a voice-over-IP capable phone (whether wired orwireless), additional difficulty can arise because such a phone may beconnected to virtually any network port (at any location) when the phoneinitiates the call.

OVERVIEW

This document describes an innovative method for conveying the locationof a wireless communication device (WCD) to an emergency service system,so as to provide the location to a PSAP and to thereby facilitateemergency service response.

The method relates to a situation where the WCD has determined itslocation using GPS technology but then enters a building where GPScoverage no longer exists (or is insufficient) and, from within thebuilding, the WCD places an emergency service call such as a 9-1-1 call.At issue in that situation is how to determine and communicate to thePSAP an indication of where in the building the WCD is currentlylocated, so that a PSAP operator can readily dispatch assistance to thatin-building location.

In accordance with the method, when the WCD enters the building anddetects that it has lost its GPS signal (i.e., that it no longer has aclear enough view of the GPS satellites in the sky), the WCD will begindead reckoning using a compass and pedometer built into the WCD, so thatcoordinates of the WCD's indoor location can be determined. Inparticular, the WCD will use its compass and pedometer to determinedirections and distances of travel of the WCD within the building. Giventhe WCD's last known GPS location coordinates, those directions anddistances of travel will then be used to geometrically compute newindoor location coordinates of the WCD, as a change in position from thelast known GPS location.

While within the building, when the WCD places a 9-1-1 call, the WCDwill then generate and transmit a SIP INVITE or other such signalingmessage that carries data indicative of the WCD's indoor locationcoordinates. Here, two options are contemplated. As one option, the WCDitself can use its determined directions and distances of travel togeometrically extrapolate from its last known GPS location, so as todetermine its current indoor location coordinates, and the WCD caninclude the determined indoor location coordinates in the SIP INVITE. Asanother option, the WCD can more simply include within the SIP INVITEits determined directions and distances, using Geographic MarkupLanguage (GML) for instance, leaving to another entity the task oftranslating the directions and distances into the WCD's current indoorlocation.

The SIP INVITE transmitted by the WCD generally functions to invokeinitiation of an RTP session between the WCD and the PSAP. For instance,an emergency service network containing the PSAP may receive the SIPINVITE, respond with a SIP 200 OK, and then receive a SIP ACK,completing establishment of an RTP session, and thereby allowing a PSAPoperator to communicate with a user of the WCD. SIP signaling like thismay flow through an IP Multimedia Subsystem (IMS) (gaining Via headersor the like along the way) that functions to apply various services tothe signaling along its way. For instance, the IMS system may include aCall Session Control Function (CSCF), which is largely an enhanced SIPproxy server that can invoke various servers or services to act upon SIPsignaling.

Pursuant to the method, the SIP INVITE will pass through an intermediaryon its way from the WCD to the emergency service system, and theintermediary will conveniently convert the WCD's indoor locationcoordinates into a description of where in the building the WCD islocated, such as a description of the room, office-cubicle, or the likewhere the WCD is located in the building. (The intermediary may alsoleave an indication of the raw indoor location coordinates in the SIPINVITE). If the SIP INVITE includes a GML indication of the WCD'sdirections and distances of travel, the intermediary may first carry outthe function of geometrically extrapolating from the WCD's last knownGPS location (which would also be specified or earlier indicated) so asto determine the WCD's current indoor location coordinates. Providedwith the WCD's indoor location coordinates, the intermediary mayestablish a description of where in the building those coordinatesreside, such as by simply referring to mapping data that correlateslocation coordinates (e.g., ranges of location coordinates) with areaswithin the building.

The intermediary will then pass along the SIP INVITE, now containing thedescription of where in the building the WCD is currently positioned,for continued transmission to the emergency service system. Thus, inaddition to invoking establishment of an RTP session for the 9-1-1 call,the SIP INVITE will advantageously convey to the emergency servicesystem a description of where in the building the WCD is currentlypositioned. And the PSAP may then conveniently present that descriptionto a PSAP operator, to facilitate emergency response.

In a further respect, the method may then involve providing theemergency service system with an updated indoor location of the WCD asthe WCD moves during the course of the 9-1-1 call, so as to keep thePSAP apprised of where the WCD is located in the building. Inparticular, during the call, the WCD may continue to apply its compassand pedometer to determine one or more further distances of travel andone or more further directions of travel. Perhaps in response to movinga threshold distance, the WCD may then generate and send to theemergency service system a SIP UPDATE message that includes anindication of the WCD's new indoor location coordinates. Again, the WCDmay include the raw (e.g., GML) indications of distances and directionsof travel, or the WCD may itself use the distances and directions oftravel to geometrically compute its new indoor location and may includethe new indoor location coordinates in the UPDATE message. As the SIPUPDATE passes through the intermediary, the intermediary will then mapthe updated indoor location to an updated description of where in thebuilding the WCD is located. Thus, the emergency service system wouldreceive the updated description, and the PSAP may present the updateddescription to the PSAP operator, to further facilitate emergencyresponse.

These as well as other aspects will become apparent by reading thefollowing detailed description with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an arrangement in which the method can beimplemented.

FIG. 2 is a flow chart depicting functions carried out in accordancewith the method.

DETAILED DESCRIPTION

An exemplary embodiment of the present method functions to communicatethe indoor location of a WCD (e.g., a cellular telephone) to anemergency service system that comprises a PSAP, where the WCD includes aGPS receiver, a compass, a pedometer, and a wireless transceiver. Inpractice, the WCD uses its GPS receiver to receive GPS satellitesignals, and the WCD then uses the received satellite signals todetermine its GPS location coordinates. In turn, the WCD then uses itscompass and pedometer as a basis to update the determined GPS locationcoordinates based on the distance(s) and direction(s) traveled by theWCD within a building, thereby establishing indoor location coordinatesof the WCD. And the WCD uses its wireless transceiver to transmit itsestablished indoor location coordinates in a SIP INVITE message seekingto set up a call to the emergency service system, where the SIP INVITEmessage invokes establishment of an RTP session between the PSAP and theWCD.

As presently contemplated, an intermediary in a SIP communication pathbetween the WCD and the emergency service system will (i) receive theSIP INVITE message, (ii) translate the indoor location coordinates to a“building portion descriptor” that describes a portion of the building(e.g., a room, office-cubicle, or other area) where the indoor locationcoordinates reside, and (iii) send the SIP INVITE message, including thebuilding portion descriptor, along to the emergency service system. Thebuilding portion descriptor may then facilitate emergency response, byletting a PSAP operator know where the emergency caller is currentlylocated within the building and thereby enabling dispatch of emergencyassistance to that in-building location.

In the exemplary method, the WCD may be programmed to periodicallyattain a GPS location fix. In that case, the act of applying the GPSreceiver to receive the GPS satellite signals and using the receivedsignals to determine GPS location coordinates of the WCD can be aninstance of the WCD periodically attaining a GPS location fix. Namely,it could be the last such instance before the WCD enters the buildingand loses its GPS signal.

Further, the act of the WCD using its compass and pedometer as a basisto update its GPS location coordinates in accordance with distance anddirection of the WCD inside the building may take various forms. Forexample, it may involve using the compass to determine (as accurately asthe WCD is capable) at least one direction of travel of the WCD,concurrently using the pedometer to determine (also as accurately as theWCD is capable) at least one distance of travel of the WCD, and usingthe at least one direction of travel and the at least one distance oftravel cooperatively to update the GPS location coordinates. Inparticular, applying simple geometric calculations, the WCD mayprogrammatically plot out its movement from its last GPS fix, so as todetermine its current location. (Further, the WCD may do this regularlybetween GPS fixes, to plan for the possibility that the WCD may beunable to attain a next GPS fix). Preferably, the GPS locationcoordinates will comprise latitude and longitude coordinates, and theindoor location coordinates will likewise comprise latitude andlongitude coordinates (as best calculated by the WCD), so thiscomputation should be straightforward.

The exemplary method may further involve the WCD itself generating theSIP INVITE message containing a specification of the WCD's establishedindoor location coordinates. In that case, the act of using the wirelesstransceiver to transmit the established indoor location coordinates in aSIP INVITE message seeking to set up a call to the emergency servicesystem may involve transmitting the SIP INVITE message, including thespecification, via an air interface from the WCD to a radio accessnetwork (RAN) serving the WCD. The SIP INVITE message may then pass fromthe RAN via a packet-switched network to an IMS CSCF and thereafter tothe intermediary, unless the CSCF itself functions as the intermediary.In turn, the intermediary may translate the specification into acorresponding building-portion descriptor, add the building-portiondescriptor to the SIP INVITE message, and transmit the SIP INVITEmessage containing the building portion descriptor via thepacket-switched network to the emergency service system. The PSAP maythen receive the building-portion descriptor (or a derivative of thebuilding-portion descriptor) and present to a human PSAP operator theindicated in-building location of the WCD, so as to facilitate emergencyresponse.

As noted above, the exemplary method may further involve carrying out aprocess to update the in-building location of the WCD during the courseof the emergency service call (i.e., anytime after initiation of thecall, or, for that matter, even after the call is finished). Inparticular, the WCD may use its compass and pedometer as a basis toupdate its indoor location coordinates in accordance with itsdistance(s) and direction(s) of movement within the building, therebyestablishing updated indoor location coordinates of the WCD. The WCD maythen use its wireless transceiver to transmit the updated indoorlocation coordinates in a SIP UPDATE message. As with the initial SIPINVITE message, the intermediary may then (i) receive the SIP UPDATEmessage, (ii) translate the updated indoor location coordinates to anupdated building-portion descriptor (which might still be the same asthe original building portion descriptor, if the WCD remains in the samein-building portion, e.g., the same room or cubicle), and (iii) send theSIP UPDATE message, including the updated building portion descriptor,along to the emergency service system. The PSAP may then receive theupdated building portion descriptor and present the updated buildingportion descriptor to the human PSAP operator, so that the updatedbuilding portion descriptor can further facilitate emergency response.

To facilitate translating the indoor location coordinates to thebuilding portion descriptor (and, likewise, the updated locationcoordinates to the updated building portion descriptor), the method mayinvolve maintaining mapping data that correlates location coordinateswith building portion descriptors, i.e., specifying ranges of indoorlocation coordinates that fall with particular building portions (e.g.,rooms, cubicles, etc.) In practice, the intermediary or another entitycould maintain such data for each of a plurality of buildings and couldselect the appropriate set of data based on the position of the WCD'slast GPS fix. Provided with such mapping data, the act of translatingthe indoor location coordinates to the building portion descriptor mayinvolve referring to (e.g., querying) the mapping data so as totranslate the indoor location coordinates to a corresponding buildingportion descriptor.

In another respect, after the WCD has attained a latest GPS fix, the WCDmay thereafter enter (e.g., be carried otherwise moved into) a building,and the WCD may detect that it is unable to receive GPS satellitesignals. In particular, the WCD may try to apply its GPS receiver toreceive signals from GPS satellites in its vicinity but the WCD mayfail, as the WCD may then lack a clear enough view of the sky.Responsive to detecting that it is unable to receive GPS satellitesignals, the WCD may then use its compass and pedometer to establish atleast one direction of travel of the WCD and at least one distance oftravel of the WCD. (Note that if the WCD is arranged to regularly useits compass and pedometer to establish directions and distances betweenGPS fixes, then the function of responsively using the compass andpedometer for this purpose may involve responsively retaining suchinformation, whereas the WCD would otherwise normally dispose of theinformation upon receiving a next GPS fix.)

While the WCD is in the building, the WCD may then receive a userrequest to initiate an emergency service call, such as by a user dialing9-1-1 or engaging a 9-1-1 speed dial function. In response, the WCD maythen responsively generate and use its wireless transceiver to transmitvia an air interface and a RAN serving the WCD, into a packet-switchednetwork, a SIP INVITE message that invokes establishment of an RTPsession between the WCD and the PSAP and that carries (a) the WCD's lastdetermined GPS location coordinates and (b) indications of the at leastone determined direction of travel of the WCD and the at least onedetermined distance of travel of the WCD. As noted above, for instance,the WCD may use GML to set forth the distance(s) and direction(s) in theSIP INVITE message.

In accordance with the exemplary method, a network server will then (i)receive the transmitted SIP INVITE message, (ii) read the GPS locationcoordinates and indications of at least one determined direction oftravel and at least one determined distance of travel from the SIPINVITE message, (iii) use the at least one determined direction oftravel and at least one determined distance of travel to update the GPSlocation coordinates so as to establish indoor location coordinates,(iv) reference mapping data to translate the indoor location coordinatesinto a building portion descriptor that describes a portion of abuilding (e.g., room, cubicle, etc.) where the indoor locationcoordinates reside in the building, and (v) transmit the SIP INVITEmessage, including the building portion descriptor, along to theemergency service system. The building portion descriptor may then bepresented to a human PSAP operator, to facilitate emergency response.

As noted above, the SIP INVITE message generated and transmitted by theWCD may pass to an IMS CSCF on its way to the emergency service system.In that case, the CSCF may itself function as the network server thatuses the WCD's indicated distances and directions of travel from theWCD's last GPS location as a basis to establish and provide thebuilding-portion descriptor. Alternatively, the CSCF could call out tothe network server to facilitate part or all of this determination.

For instance, the CSCF could query the network server, to have thenetwork server determine the in-building location coordinates andtranslate those coordinates to a building-portion descriptor, and theCSCF could then insert the building-portion descriptor into the SIPINVITE before sending the SIP INVITE to the emergency service system.Alternatively, the CSCF could simply send the SIP INVITE message to thenetwork server, the network server could establish the building-portiondescriptor, add the building-portion descriptor to the SIP INVITEmessage, and send the modified SIP INVITE message back to the CSCF. TheCSCF could then send the SIP INVITE message along its way to theemergency service system. Still alternatively, the network server coulddirectly transmit the modified SIP INVITE message to the emergencyservice system rather than sending it back to the CSCF for transmission.

Also as noted above, the method may involve conveying to the emergencyservice system one or more updates of the WCD's in-building locationduring the course of the RTP session. In particular, the WCD may use itscompass and pedometer to establish at least one further direction oftravel of the WCD and at least one further distance of travel of theWCD, and the WCD may use its wireless transceiver to transmit via theair interface and RAN, into the packet-switched network, a SIP UPDATEmessage carrying the at least one further direction of travel and atleast one further distance of travel (e.g., using GML). The networkserver may then (i) receive the transmitted SIP UPDATE message, (ii)read the at least one further direction of travel and at least onefurther distance of travel from the SIP UPDATE message, (iii) use the atleast one further direction of travel and at least one further distanceof travel to update the indoor location coordinates so as to establishupdated indoor location coordinates, (iv) reference the mapping data totranslate the updated indoor location coordinates into an updatedbuilding portion descriptor, and (v) transmit the SIP UPDATE message,including the updated building portion descriptor, along to theemergency service system. The updated building portion descriptor maythen be presented to the human PSAP operator, to further facilitateemergency response.

In this embodiment, like that described above, the mapping data thatcorrelates location coordinates with building portion descriptors can bemaintained at the network server. Alternatively, the mapping data couldbe maintained elsewhere and made accessible to the network server.

In another respect, the exemplary method may function to convey locationof a WCD to an emergency service system including a PSAP. In practice,the WCD may apply its GPS receiver to receive GPS satellite signals, andthe WCD may use the received signals to periodically attain GPS locationfixes (location coordinates of the WCD). In this method, after the WCDattains a latest GPS location fix, the WCD then enters a building wherethe WCD lacks a clear enough view of the sky to attain a next GPSlocation fix. Once in the building, the WCD then applies its compass andpedometer to determine at least one direction of travel of the WCDwithin the building and at least one distance of travel of the WCDwithin the building, and the WCD uses the determined direction(s) anddistance(s) cooperatively to update the location coordinates of thelatest GPS location fix so as to establish indoor location coordinatesof the WCD.

While the WCD is in the building, the WCD then receives from a user ofthe WCD an emergency service call request, and the WCD responsivelytransmits, via an air interface to a RAN for transmission in turn to theemergency service system, a Session Initiation Protocol (SIP) INVITEmessage seeking to set up the emergency service call, including withinthe SIP INVITE message the established indoor location coordinates. Inaccordance with the method, an intermediary in a communication pathbetween the WCD and the emergency service system then (i) receives theSIP INVITE message, (ii) translates the indoor location coordinates to adescriptor of a portion of the building, and (iii) sends the SIP INVITEmessage, including the descriptor of the portion of the building, alongto the emergency service system. The descriptor of the portion of thebuilding can then be presented to a human PSAP operator, so as tofacilitate emergency response.

Referring to now the figures, FIG. 1 is a simplified block diagramdepicting an arrangement in which the present method can be implemented.It should be understood, of course, that variations from this and otherarrangement shown and described herein are possible. For instance,elements can be added, removed, combined, distributed, re-ordered, orotherwise modified. Further, it should be understood that functionsdescribed herein as being carried out by a device, server, and/or otherentity can be carried out by one or more a suitably programmedprocessors or by any combination of hardware, software, and/or firmware.

As shown in FIG. 1, the exemplary arrangement includes a WCD 12, such asportable handheld cell phone, a personal digital assistant, or anotherdevice that is capable of initiating an emergency service call, such asa 9-1-1 call. The WCD 12 is served by a cellular radio access network(RAN) 14 operating according to any air interface protocol now known orlater developed, examples of which currently include CDMA (e.g., 1xRTT,1xEV-DO), iDEN, TDMA, AMPS, GSM, GPRS, UMTS, EDGE, WiMAX (e.g., IEEE802.16), LTE, microwave, satellite, MMDS, Wi-Fi (e.g., IEEE 802.11), andBluetooth.

As shown, the WCD 12 includes a GPS receiver 16 (for receiving GPSsatellite signals), a cellular wireless transceiver 18 (forcommunicating with the RAN), a processor (one or more processors) 20,and data storage 22 containing program instructions executable by theprocessor to carry out various functions described herein. Further, theWCD 12 includes a compass 24 and a pedometer 26, which can be used incombination to facilitate dead reckoning so as to keep track of theWCD's location between GPS location fixes or when the WCD loses GPScoverage. In practice, the compass 24 can be an electronic compass orother sensor of a type well known in the art that indicates direction oftravel with reference to magnetic north, and the pedometer 26 can be anysort of meter (e.g., an electro-mechanical pendulum or ball-bearingbased pedometer) that indicates a distance of travel. As the pedometermay measure distance of travel in terms of number of steps taken by theperson carrying the WCD, the pedometer 26 or WCD 12 is preferablycalibrated in advance to account for the average stride of the user, sothat the WCD can convert a count of steps into a fairly accurateapproximation of distance traveled.

As further shown, the exemplary arrangement includes a building 30 (suchas a home, office, or theater for instance) into which the WCD 12 can becarried, with a possible path of travel of the WCD within the buildingshown by dashed lines and dots. The example building 30 is representedillustratively by a floor plan that shows various indoor buildingportions or areas (such as rooms or cubicles, for instance) into whichthe WCD may be carried. In the exemplary embodiment, the WCD 12 caninitiate an emergency service call from anywhere within the building.Aside from merely reporting to the PSAP the location of the building inwhich the WCD is located, it is also important to inform the PSAP wherein the building the WCD is located, so that the PSAP can provideemergency assistance at that particular in-building location.

The exemplary arrangement further includes a global positioning system(GPS) having a plurality of positioning satellites 32, one of which isshown by way of example. In practice, when the WCD 12 is outside of thebuilding 30 and has a clear view of the sky, the WCD 12 can receivesignals from GPS satellites. Applying well known location-determinationprinciples, the WCD can interact with a positioning system (not shown)operated by the WCD's cellular wireless carrier, to obtainsatellite-assistance data corresponding with the WCD's general location(where the general location can be determined by triangulation usingcellular base station signal measurements). The satellite assistancedata indicates which satellites should in theory be orbiting above theWCD's current location, such that the WCD should be able to receivesignals from the satellites. In accordance with the satellite assistancedata, the WCD can then tune to the various satellites and receivesignals, and then by itself or through further interaction with thenetwork-based positioning system, can determine with great accuracy thelatitude and longitude coordinates of the WCD's current position. Othermethods of attaining a GPS fix can be used as well.

As noted above, the WCD may be programmed to periodically obtain a GPSlocation fix, Once the WCD enters building 30, however, the WCD may lostits GPS coverage, i.e., its ability to receive GPS satellite signals.Thus, while within the building, the WCD may be unable to obtain anotherGPS location fix.

To facilitate determine of the WCD location while indoors or between GPSlocation fixes, the WCD is preferably programmed to engage in deadreckoning using its compass 24 and pedometer 26. More particularly, theWCD may determine its indoor location coordinates through dead reckoningfrom its last known GPS location coordinates. In particular, the WCD maygather measurements of its distance(s) and direction(s) of travel withinthe building and, applying simple geometric calculations, compute (orapproximate) its current geographic location coordinates within thebuilding, by extension from its last known location coordinates.Alternatively, the WCD may simply maintain a record of its last knownlocation coordinates (e.g., GPS coordinates) and its distance(s) anddirection(s) of travel within the building, so as to enable anotherentity to geometrically compute the WCD's current geographic locationcoordinates within the building.

As further illustrated, the exemplary arrangement includes an emergencyservice system 34 comprising a PSAP 36, which WCD 12 can call to reportan emergency and to seek emergency assistance. (Just as well, the methodcould be carried out for calls of other types placed to otherendpoints.) In practice, when the WCD 12 places an emergency servicecall, call setup signaling passes from the WCD (or an entity operatingon behalf of the WCD) to the emergency service system 34. For instance,to initiate the call, the WCD may generate and send a SIP INVITE messageto the emergency service system 34 and may then engage in further SIPsignaling with the emergency service system to complete setup of an RTPsession through which a WCD user can communicate with a PSAP operator.Further, additional SIP signaling, such as one or more SIP UPDATEmessages, may pass from the WCD to the emergency service system duringthe course of the call. A SIP message, or other signaling message, maychange form as it travels from one point to another. For instance, a SIPmessage may gain Via headers as it passes through various networkelements.

When the WCD sends a SIP or other signaling message to the emergencyservice system when the WCD is within the building 30, the WCD willpreferably include within the signaling message an indication of theWCD's indoor location, for use to facilitate emergency assistance. Asindicated above, for instance, the indication of indoor location that isincluded in the signaling message could be geographic locationcoordinates (determined through dead reckoning for instance) or more rawdata such as (i) the WCD's last known location coordinates and (ii)distance(s) and directions(s) traveled by the WCD within the building.

In the exemplary embodiment, an intermediation system 40 is thenprovided within the signaling communication path (and/or, in the eventlocation data is conveyed in the bearer path, then within the bearerpath) between the WCD and the emergency service system 22, to facilitateconversion of such indoor location information into a moreunderstandable description of the portion of the building in which theWCD is located. The intermediation system 40 may take various forms (andcould in fact be located within the RAN), an example of which is an IMSsystem including a CSCF and one or more application servers arranged tooperate on signaling messages passing through the system. In operation,when the a signaling message is going to pass through the CSCF, the CSCFcan analyze the message and determine that location translation isnecessary (e.g., by determining that the message relates to an emergencyservice call, and responsively determining that location data in themessage should be translated to a building portion description). TheCSCF may then perform the translation or invoke another server toperform the translation, as described above for instance.

As shown, the intermediation system 40 preferably includes a networkcommunication interface 42, a processor (e.g., one or more processors)44, and a set of mapping data 46 that correlates indoor locationcoordinates with particular building portions. For instance, the mappingdata 46 may comprise a table that correlates ranges of locationcoordinates with particular rooms, cubicles or other zones within abuilding and that provides for each building portion a textualdescription, such as room number, zone number, or the like. The buildingportion description is preferably sufficient to help to direct emergencyservice personnel, such as police officers, fire fighters, or medicalservice people, to the appropriate area within the building.

In operation, when a signaling message such as a SIP INVITE or SIPUPDATE passes through the intermediation system on its way from the WCD(or an entity operating on behalf of the WCD) to the emergency servicesystem, the intermediation system may read from the signaling messagethe WCD's indoor location coordinates and/or the WCD's last knownlocation coordinates and the distance(s) and direction(s) travelled bythe WCD within the building. The intermediation system may thenreference the mapping data 46 in order to convert that data into adescription of the portion of the building in which the WCD is currentlylocated. And the intermediation system may insert that building-portiondescription in the signaling message and send the signaling messagealong its way to the emergency service system. That way, the emergencyservice system will conveniently receive the building portiondescription and can present it to a PSAP operator to facilitateemergency assistance.

FIG. 2 is next a flow chart depicting functions that can carried out inaccordance with the present method. As shown in FIG. 2, at step 50, theWCD 12 attains a GPS location fix while it is outside and within GPScoverage. At step 52, the WCD 12 then moves into and through thebuilding 30, where it lacks GPS coverage. At step 54, as the WCD 12moves, the WCD applies its compass 24 and pedometer 26 to determine itsdistance(s) and direction(s) of travel as it reaches a location withinthe building. At step 56, the WCD then receives from its user a requestto initiate an emergency service call. Consequently, at step 58, the WCDgenerates and transmits a SIP INVITE (or other such signaling message),including within the message an indication of the WCD's indoor location.As noted above, the indication of indoor location that the WCD includesin the signaling message can be indoor geographic location coordinatesthat the WCD establishes by dead reckoning by using measurements fromits compass and pedometer to facilitate geometric extension from itslast determined location coordinates. Alternatively, the indication canbe more raw data including its last determined location coordinates andits measured distance(s) and direction(s) of travel within the building.

At step 60, the intermediation system (such as an IMS system) 40receives the SIP INVITE and reads the indoor location indication fromthe message. At step 62, the intermediation system then translates theindoor location indication into a building-portion description,preferably a textual description of the portion of the buildingencompassing the WCD's indicated indoor location. At step 64, theintermediation system then passes the SIP INVITE along to the emergencyservice system. And at step 66, the emergency service system presentsthe building-portion description to a PSAP operator, to facilitateemergency assistance.

At step 68, a similar process can then be repeated with respect toupdated in-building location as the WCD moves within the building duringthe call, thereby providing the PSAP operator with an update of theWCD's location and further facilitating emergency assistance.

An exemplary embodiment has been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto this embodiment without departing from the true scope and spirit ofthe invention, which is defined by the claims, including theirequivalents.

1. A method of conveying location of a cellular wireless communicationdevice (WCD) to an emergency service system comprising a Public SafetyAnswering Point (PSAP), the WCD including a GPS receiver, a compass, apedometer, and a wireless transceiver, the method comprising: the WCDapplying the GPS receiver to receive GPS satellite signals, and the WCDusing the received signals to determine GPS location coordinates of theWCD; the WCD thereafter entering a building and detecting that the WCDis unable to receive GPS satellite signals, and, responsive to beingunable to receive GPS satellite signals, the WCD then using the compassand pedometer to establish at least one direction of travel of the WCDand at least one distance of travel of the WCD; while in the building,the WCD receiving a user request to initiate an emergency service call,and the WCD responsively using the wireless transceiver to transmit viaan air interface and radio access network serving the WCD, into apacket-switched network, a Session Initiation Protocol (SIP) INVITEmessage carrying (a) the GPS location coordinates and (b) indications ofthe at least one determined direction of travel of the WCD and the atleast one determined distance of travel of the WCD; a network server (i)receiving the transmitted SIP INVITE message, (ii) reading the GPSlocation coordinates and indications of at least one determineddirection of travel and at least one determined distance of travel fromthe SIP INVITE message, (iii) using the at least one determineddirection of travel and at least one determined distance of travel toupdate the GPS location coordinates so as to establish indoor locationcoordinates, (iv) referencing mapping data to translate the indoorlocation coordinates into a building portion descriptor that describes aportion of a building where the indoor location coordinates reside inthe building, and (v) transmitting the SIP INVITE message, including thebuilding portion descriptor, along to the emergency service system,wherein the SIP INVITE message invokes establishment of a Real-timeTransport Protocol (RTP) session between the PSAP and the WCD, wherebybuilding portion descriptor is presented to a human PSAP operator andthereby facilitates emergency response.
 2. The method of claim 1,wherein applying the GPS receiver to receive the GPS satellite signalsand using the received signals to determine GPS location coordinates ofthe WCD is an instance of the WCD periodically attaining of GPS locationfix.
 3. The method of claim 1, wherein the GPS location coordinatescomprise latitude and longitude coordinates, and wherein the updatedlocation coordinates comprise latitude and longitude coordinates.
 4. Themethod of claim 1, further comprising the WCD generating the SIP INVITEmessage carrying the UPS location coordinates and indications of the atleast one determined direction of travel of the WCD and the at least onedetermined distance of travel of the WCD.
 5. The method of claim 1,further comprising the SIP INVITE message passing to an IP MultimediaSubsystem (IMS) Call Session Control Function (CSCF) and thereafter tothe network server.
 6. The method of claim 1, further comprising, duringthe RTP session, while the WCD is still in the building: the WCD usingthe compass and pedometer to establish at least one further direction oftravel of the WCD and at least one further distance of travel of theWCD; the WCD using the wireless transceiver to transmit via the airinterface and radio access network serving the WCD, into thepacket-switched network, a SIP UPDATE message carrying the at least onefurther direction of travel and at least one further distance of travel;the network server (i) receiving the transmitted SIP UPDATE message,(ii) reading the at least one further direction of travel and at leastone further distance of travel from the SIP UPDATE message, (iii) usingthe at least one further direction of travel and at least one furtherdistance of travel to update the indoor location coordinates so as toestablish updated indoor location coordinates, (iv) referencing themapping data to translate the updated indoor location coordinates intoan updated building portion descriptor, and (v) transmitting the SIPUPDATE message, including the updated building portion descriptor, alongto the emergency service system, wherein the updated building portiondescriptor is presented to the human PSAP operator and thereby furtherfacilitates emergency response.
 7. The method of claim 6, furthercomprising using Geographic Markup Language (GML) to provide the atleast one further direction of travel and at least one further distanceof travel in the SIP UPDATE message.
 8. The method of claim 1, furthercomprising: maintaining the mapping data at the network server, whereinthe mapping data correlates location coordinates with building portiondescriptors.
 9. The method of claim 1, wherein the portion of thebuilding comprises a portion selected from the group consisting of aroom and an office-cubicle.